J, M. BEAL 159 



florum var. eximium) the region of response was limited largely to the 

 cells of the epidermis and outer cortex in the immediate vicinity of the 

 leaf axils adjacent to the surface of application. Adventitious roots were 

 rarely formed. The epidermal cells of the stem immediately above the 

 axil elongated radially, while the outer cortical cells centripetal to as 

 well as slightly below them enlarged and in the course of about five 

 days began dividing. This marked the initiation of the region at which 

 buds later developed. Neither buds nor bud primordia were present in 

 these leaf axils at the time of treatment. The groups of meristematic 

 cells in the leaf axils divided repeatedly, accompanied by radial divisions 

 of the cells of the epidermis over them. The subsequent growth of their 

 derivatives resulted in a hump of cells which through further develop- 

 ment and differentiation became a bud. As many as three buds may 

 develop in one axil. If permitted to grow on the plant for 8 to 10 weeks, 

 the induced buds became bulbils with roots at their bases. Bulbils were 

 removed from the parent plant and grown separately. No visible ana- 

 tomical differences were observed which could be used in explaining 

 the differences in the behavior of the three species. 



Responses to Other Growth Substances 



A number of other growth substances have been applied to the red 

 kidney bean. Indolebutyric acid (20) produced apical tumors similar to 

 those resulting from indoleacetic acid, but with fewer, thicker roots in 

 the upper zone, more roots i cm. or so below the treated surface, and 

 several tiers of roots between these two regions. Naphthaleneacetic acid 

 (20) resulted in the formation of apical tumors with greater and more 

 uniform diameter for a distance of about i cm. below the cut surface, 

 where a circle of large root primordia was formed, each primordium over 

 one of the main vascular bundles. The responses to tryptophan (22) 

 are less vigorous but similar insofar as the responsive tissues are concerned. 

 No adventitious roots developed but abundant anastomosing vascular 

 strands were differentiated, mostly from derivatives of the endodermis. 

 Whether these effects are due to indoleacetic acid derived from trypto- 

 phan is not wholly certain. Histological studies indicate they may not 

 be; biochemical determination of material in situ must be made. An 

 extract of maize pollen (28) applied to bean stems produced responses 

 similar to those from tryptophan. Tetrahydrofurfurylbutyrate (29) pro- 

 duced Uttle or no effect on epidermis, cortex, pericycle, or cambium, 



